In pea plants the allele B for round seeds is dominant to the allele b for wrinkled seeds. Two plants that each carry one B allele and one b allele are crossed. What phenotype ratio is expected among the offspring?

Explication

Each parent passes on either B or b, so four equally likely combinations arise, and three of them contain at least one B and therefore look round. A 1 to 2 to 1 figure counts the pairs of alleles instead of the appearances, which answers a different question about the same cross.